Technical Field
The present disclosure relates to a sensor that detects force acting around a rotation axis, a driving mechanism that uses the sensor, and a robot.
Description of the Related Art
In recent years, articulated robots have been used in various industrial product assembly lines. However, there are also many processes that are difficult to perform with articulated robots. For example, articulated robots are widely used particularly in processes in which loads from several hundred grams to several kilograms are applied in automotive-component assembly lines. In contrast, for processes in which loads on components need to be on the order of grams, for example, assembly of workpieces made of a soft material, a lightweight material, or a low-strength material, and processes of close tolerance fitting, there are various difficulties in performing with articulated robots.
Such workpieces made of a soft, lightweight, or low-strength material should not be subjected to large force to prevent damage and deformation of the workpieces. In operating this type of workpiece with an articulated robot, force that acts on the workpiece via joints and links needs to be accurately controlled.
In particular, of forces that act on the links of a robot arm, a force that needs to be measured to accurately control driving of the articulated robot is torque acting around the drive axes of the joints.
Close tolerance fitting of workpieces made of a soft, lightweight, or low-strength material using an articulated robot needs high-accuracy, high-resolution sensors at the joints of the arms.
For a configuration in which the amount of deformation of an elastic member that transmits a driving force is detected using a detection head, the amount of deformation relative to the force needs to be increased to enhance the resolution of the torque sensor. However, increasing the amount of deformation of the elastic member relative to the same force can decrease the rigidity of the torque sensor in a torque detecting direction. The decrease in the rigidity of the torque sensor will decrease the rigidity of the joint mechanism and the driving control range of the articulated robot, which can decrease the controllability. The decrease in the rigidity of the joint mechanism is reduced as much as possible also with a high-resolution torque sensor that detects force acting on a joint.
Japanese Patent Laid-Open Nos. 10-286789 and 2012-189516 disclose configurations including guide members to ensure high rigidity of the joint mechanisms or in consideration of cross-axis force acting on the joints (force acting in five directions except about the driving axes of the joints). For example, in Japanese Patent Laid-Open No. 10-286789, a bearing is provided as a guide member for supporting cross-axis force at a relative displacement portion of two links connected with a joint. A torque sensor disclosed in Japanese Patent Laid-Open No. 2012-189516 has a configuration in which a guide member that prevents an elastic member from being deformed in a cross-axis direction is provided on the elastic member.
However, a guide member, such as a bearing, for ensuring sufficient rigidity of the joint, or supporting cross-axis force will act as a load on driving around the driving axis of the joint. For example, retaining and restricting the torque sensor with the guide member will influence the torque around the joint driving axis, which may hinder accurate detection of the torque around the joint driving axis to be detected by the torque sensor.
For that reason, to accurately detect the torque around the joint driving axis with the torque sensor, it is necessary to support the cross-axis force with the elastic member of the torque sensor without using the guide member. In other words, to enhance the torque detection accuracy, no guide member is used, and a decrease in rigidity in the cross-axis direction needs to be prevented.